The ivory trade was formally disapproved of in Islam but as an extravagance rather than out of animal welfare considerations. The renowned Saharan Tuareg with the traditional headgear were associated especially with the salt trade.
The part of the basin of the Niger River bordering the southern Sahara (and known in Arabic as the Sahal (beach/coast)) was influenced by Muslims from at least the 10th Century. Bakri from 11th Century Spain was an Arab historian of this area as was the 12th Century Tunisian (and Norman Italian) Arab, Idrisi (a descendent of the founder of the Idrisid dynasty). From them we know that Muslim merchants were allowed by the local king of what is now (roughly) Ghana to build and worship at a mosque there. We also learn from them that a pattern of conversion of first elites, who learned Islam from learned merchants and sometimes Sufi mystics, and then their subordinates developed in the local West African societies.
As with the Maghreb, the hajj was enthusiastically attended and participation conferred great prestige on the hajji when back home in West Africa.
Mutual visits also forged significant links between West Africa and the rest of the Islamic world. Nevertheless, Ibn Battuta noted in the 14th Century that Islam was still predominantly practiced then by the elites.
We know from the work of a Muslim historian in Niger that the locals preferred to add Islam to local customs rather than replace the old customs completely. He notes the absence of the early influence of the Muslim jurisprudents as a problem for the 'proper' local development of Islam (as he saw it) and sees that as having produced the reformist (and jihadist) movements of the 19th Century, which sought to introduce the stricter form of Islam lacking in West Africa. Another view is that early West African Islam benefited from lacking the strictures of the legalism which developed elsewhere.